The invention concerns generally the technological field of electromechanical implementation of a radio device, like a portable radio transceiver. Especially the invention concerns both antenna structures and the structures that are used for shielding microelectronic components to achieve certain EMC or electromagnetic compatibility.
Modern radio transceivers comprise a PCB or printed circuit board onto which a number of microelectronic and radio frequency components are soldered. To shield the components against electromagnetic interference from external sources, and to keep the stray electromagnetic fields generated by the components from causing interference elsewhere, the electromechanical structure of the radio transceiver must define a number of enclosures with conductive walls that surround the components and have good contacts to the general ground potential level of the radio transceiver. A number of lead-ins are provided in the walls to pass signals in a controlled way between the components of the radio transceiver.
FIG. 1 is an exploded cross-sectional view that shows schematically a known structural arrangement which is built on a PCB 101 with a number of contact strips 102 and contact pads 103 on its upper surface. FIG. 2 shows the same structure in an assembled position. Microelectronic and radio frequency components 104 are soldered onto contact pads 103 and surrounded by a conductive frame 105 which comes into contact with conductive, grounded strips 102 on the surface of the PCB 101. A planar lid 106 is placed on top of the frame 105 and attached into place by soldering or by other means. An outer cover 107 protects the whole arrangement and gives it a desired outer appearance.
FIGS. 1 and 2 show also a known way of building an internal antenna to the radio transceiver. The antenna type in question is the well-known PIFA or Planar Inverted-F antenna which comprises on the surface of the PCB a ground plane 108, a grounding pad 109 (which may also be an integral part of the ground plane) and a feeding pad 110 from which there is a transmission line (not shown) to a duplex filter or other radio frequency component that forms the part of the radio transceiver which in the signal propagation sense is closest to the antenna. The PIFA structure comprises further a planar radiator 111 from which there extend a grounding pin 112 and a feeding pin 113 towards the PCB 101. There are many ways of implementing the planar radiator, of which FIGS. 1 and 2 show a thin conductive sheet that is attached to the inner surface of the outer cover 107. The grounding and feeding pins 112 and 113 are integral with the radiator sheet since they have been cut from the same material and just bent into an essentially 90 degrees angle against the plane of the radiator.
The prior art structure described above involves some problems. For example, the conductive tracks on the PCB that couple the feeding pad 110 to the radio frequency component closest to the antenna become easily relatively long, which causes attenuation and distortion especially to the weak radio frequency oscillations that represent a received signal. Also if soldering or some other difficultly reversed method is used to attach the shielding frame 105 and its lid 106 to each other and to the PCB, it becomes difficult and unproductive to check or service the components within the EMC shielding enclosure if needed.
It is an object of the present invention to provide an electromechanical structure for a radio transceiver device which combines easy inspection and servicing of components, structural compactness and good protection against electromagnetic interference.
The objects of the invention are achieved by using a single conductive plate at least partly both as a detachable lid for an EMC shielding enclosure and as a ground plate for an antenna.
In its first embodiment the electromechanical structure according to the invention for a portable radio device comprises a circuit board, a number of components attached to the circuit board, a conductive shield for enclosing the components and an essentially planar antenna radiator. In this embodiment the structure is characterized in that a part of the conductive shield is essentially planar and adjacent to the antenna radiator in order to function as a ground plane for the antenna radiator.
In its second embodiment the electromechanical structure according to the invention for a portable radio device comprises an essentially planar antenna radiator and an essentially planar conductive element adjacent to the antenna radiator in order to function as a ground plane for the antenna radiator. In this embodiment the structure is characterized in that the essentially planar conductive element is additionally arranged to function as a part of a conductive shield for enclosing certain electronic components of the portable radio device into an EMC shielding enclosure.
The lid which was formerly used to cover an EMC shielding enclosure is essentially planar, conductive and grounded. Also the antenna ground plate known as such from prior art antenna constructions is essentially planar, conductive and grounded. According to the present invention, structural and functional advantages are gained by using the same essentially planar, conductive and grounded element at least partly both as a lid that covers an EMC shielding enclosure and an antenna ground plate. Not only is it possible to produce the radio transceiver structure with one less part than before, but also PCB space is saved if virtually no extra space has to be allocated to the antenna parts and antenna-related transmission lines. Additionally, if and when the component that is closest to the antenna in the signal propagation sense is placed within this particular EMC shielding enclosure, it becomes very easy to minimize the length of the transmission line between it and the antenna feeding point.
According to an advantageous embodiment of the invention the lid/grounding plate is not separataly soldered or in any way permanently attached to the frame of the EMC shielding enclosure, but it only comes in contact therewith at a certain final assembly stage, preferably the stage where the fully equipped and functionally tested PCB with all electronic and radio frequency parts of the radio transceiver is placed within the appropriate outer cover part. This ensures full serviceability to the components within the EMC shielding enclosure during manufacturing, and even later during the service life of the radio transceiver.